Who Else Has Passed A Drug Test In One Day?

Okay so I am pretty exited because I just passed a drug test in one day without using anything to alter it. It was just straight up pee. I smoked all day yesterday. I probably smoked close to 4 grams. The next day my parents randomly ask me to do a drug test. At this point im freaking out because my mom is phyco and would send me to drug rehab if I failed. I swear to god. Anyway, I told them I didnt have to pee so I could buy more time. They gave me 30 minutes to drink water so I could pee. During those 30 minutes my parents went to take the dogs on a walk and while they were gone I drank probably about 15 or 16 full glasses of water. When they came back they had me pee in the cup and I peed pretty much clear (with a little bit of yellow) and passed the test with just my pee and nothing else. Can someone explain how is that even possible! Prior to that test I had been smoking strong everyday for about a month. Im a very lucky person because I avoided going to rehab for smoking weed. How ridiculous does that sound..